1. Field of the Invention
The embodiments disclosed herein relate to an inverter device and a motor drive system.
2. Description of the Related Art
There has been available a winding switching method enabling a wide-area operation from a low speed area to a high speed area by switching the armature windings of an alternating-current (AC) motor to switch the electric characteristics of the AC motor.
In this winding switching method, to reduce a shock caused by switching of the windings, measures are taken, such as prohibiting switching of the windings in a circumstance where the number of rotations of the AC motor is rapidly changing (see Japanese Unexamined Patent Application Publication No. 06-225588).
However, when such measures are taken, the efficiency is low in the case where the speed is consecutively increasing from low speed to high speed, for example, and a sufficient torque is not obtained. To this end, the present applicant has proposed in Japanese Unexamined Patent Application Publication No. 2010-22165 an inverter device capable of reducing a shock caused by switching of the windings even during acceleration or deceleration.
The inverter device described in Japanese Unexamined Patent Application Publication No. 2010-22165 calculates a d-axis current command correction value, which is a correction value of a d-axis current command, when a voltage command exceeds a maximum voltage value that can be output to an AC motor, and performs field weakening control that corrects the d-axis current command by using the calculated d-axis current command correction value. In this field weakening control, the inverter device described in Japanese Unexamined Patent-Application Publication No. 2010-22165 preliminarily calculates a d-axis current command correction value prior to switching of the windings, and, at a winding switching timing, corrects the d-axis current command by using the pre-calculated d-axis current command correction value.
Accordingly, a delay in calculating a d-axis current command correction value, which is one of the causes of a shock caused by switching of the windings, can be removed, and smooth winding switching becomes possible even during acceleration or deceleration.
However, because the inverter device described in Japanese Unexamined Patent Application Publication No. 2010-22165 preliminarily calculates a d-axis current command correction value prior to switching of the windings and corrects a d-axis current value by using the d-axis current command correction value at a winding switching timing, the processing is complicated.